Metal coated with polyvinylidene fluoride coating compositions

ABSTRACT

A coating composition containing polyvinylidene fluoride, an epoxy resin, an aminoplast resin, and optionally, TiO2 or zirconium silicate and zinc, all in an organic liquid carrier, useful for lining water heater tanks and industrial containers.

United States Patent 11 1 Vasta 1 METAL COATED WITH POLYVINYLIDENEFLUORIDE COATING COMPOSITIONS Inventor: Joseph A. Vasta, Woodburg, NJ.

Assignee: E. 1. du Pont de Nemours and Company, Wilmington, Del.

Filed: Oct. 5, 1973 Appl. No.: 403,865

Related US. Application Data Division of Ser. No. 229,509, Feb. 25,1972, Pat. No. 3,784,506, which is a continuation-in-part of Ser. Nos.174,280, Aug. 23, 1971, abandoned, and Ser. No. 37,064, May 13, 1970,abandoned.

US. Cl 117/132 A, 112/74, 112/96, 112/97, 117/132 BE, 117/132 BF,117/132 CF, 117/161 LN, 117/161 UF, 117/161ZB Int. Cl B32b 15/08, C09d3/78 Field of Search 260/39 R, 834, 900, 37 EP;

117/132 CF, 132 A, 132 B, 132 BE, 132 BF, 161 L, 161 LN, 161 UP, 161 Z8,97, 96, 74

References Cited UNITED STATES PATENTS 3/1966 Kusiak 117/132 CF FOREIGNPATENTS OR APPLICATIONS 651,190 10/1962 Canada 260/834 OTHERPUBLICATIONS Lee et a1., Handbook of Epoxy Resins,"

McGraw-Hill Book Co., pp. 14-3, 14-4, (1967).

Primary Examiner-Harry J. Gwinnell [57] ABSTRACT A coating compositioncontaining polyvinylidene fluoride, an epoxy resin, an aminoplast resin,and optionally, T10 or zirconium silicate and zinc, all in an organicliquid carrier, useful for lining water heater tanks and industrialcontainers.

3 Claims, No Drawings METAL COATED WITH POLYVINYLIDENE FLUORIDE COATINGCOMPOSITIONS CROSS-REFERENCE TO RELATED APPLICATIONS This application isa divisional of application Ser. No. 229,509, now U.S. Pat. No.3,784,506, filed Feb. 25, 1972, which in turn is a continuation-in-partof applications Ser. No. l74,280, filed Aug. 23, l97land Ser. No.37,064, filed May 13, l970,both now abandoned.

BACKGROUND OF THE INVENTION As every homeowner knows, the interiorsurfaces of many water heater tanks manufactured for home use are coatedwith glass to minimize corrosion.

Glass, however, has many failings. First of all, it is brittle andsubject to mechanical failure. Secondly, it dissolves slowly in waterand so the lining thins over the years to the point where corrosionbegins Third, glass itself is porous and permits water to come incontact with the metal through the pores, which causes corrosion.Lastly, a glass tank requires an anode for long life. Besides all this,lining a water heater tank with glass is an expensive operation becauseof the high temperature required in the fusion step and consequent needfor gauge metal.

I have found that these failings are minimized and that a tough,impermeable, longlasting, organic polymeric coating can be applied to awaterheater tank with far less cost by using my compositions. Inaddition, my coating gives a water heater tank with a useful lifecomparable to that of a glass tank, without use of an anode.

SUMMARY OF THE INVENTION My coating compositions contain polyvinylidenefluoride, an epoxy resin and an aminoplast resin, all in an organicliquid carrier.

The polyvinylidene fluoride I use in my compositions is of the typedescribed in U.S. Pat. No. 2,435,537. Such resins are freely availableon the market. The resin Iprefer to use is Kynar, sold by PennwaltChemical Company. Polyvinylidene fluoride is ordinarily present in mycompositions at a concentration of from percentthrough about 90 percent,preferably 25-75 percent and even more preferably about 50 percent, byweight of the binder components.

The epoxy resins I use in my compositions can be any of the well-knowncondensation products of bisphenol A or bisphenol F withepichlorohydrin, and having gram epoxy equivalent weights of 300-8000,preferably 400-4000, even more preferably 400-2500. The epoxy resins Iespecially prefer for the quality of the finishes obtained when one usesthem are the Epon 1001 through 1009 resins, sold by-the Shell ChemicalCompany. The epoxy resins are ordinarily present in my compositions atconcentrations from about 5 percent through about 90 percent, preferably-60 percent and even more preferably about 35 percent, by weight of thebinder components.

para,para-isopropylidene diphenol 4,4'-dihydroxydiphenylmethane Theaminoplastresins I use in my compositions are condensates offormaldehyde with melamine, urea, benzoguanamine ormelaminetoluenesulfonamide. These resins can be prepared according tothe directions in U.S. Pat. Nos. 2,197,357, 2,508,875 and 2,191,957. Iprefer to use a benzoguanamineformaldehyde resin because of the qualityof the coating obtained when it is used.

The aminoplast resins are ordinarily present in my compositions atconcentrations of from- 5 percent through about 90 percent, preferably5-25 percent, even more preferably about 15 percent, by weight of thebinder components.

The organic liquid I use as a carrier in my compositions is in the usualcase a mixture of those which find their way into the compositions assolvents or carriers for the solid and/or resinous components. Theseorganic liquids are usually diacetone alcohol, aliphatic and aromatichydrocarbons, ketones and the like, or mixtures of these. Generallyspeaking, the nature of these liquids is unimportant; it is necessaryonly that they be compatible with the components of the composition andthat they have no adverse effects on the coating itself.

While it is not necessary that my compositions contain a pigment, I havefound that the integrity of the resulting films is improved if thecompositions contain from about 5 through 100 percent, preferably 25-75percent, even more preferably about 50 percent, by weight of the bindercomponents, of TiO I have also found that the corrosion protectionconferred by my compositions is enhanced if they contain from about 50through about 900 percent, preferably 100-700 percent, and even morepreferably about 85-350 percent, by weight of the binder components, ofparticulate zinc. The zinc can be in powder or flake form. When thesecompositions are used, water heaters need contain no magnesium anodes.

The stability and blister resistance of coatings derived from mycompositions are also enhanced by adding to the compositions from about0.1 through about 5 percent, by weight of the binder components, of ahydrophobic silica such as that sold by the Philadelphia Quartz Companyas Quso." I prefer to use from about 0.5 to about 1.5 percent, even morepreferably 1 percent, of this material.

In addition, the corrosion protection provided by my compositions issignificantly improved if they contain from 5 through about 100 percentof zirconium silicate, preferably 25 through percent, even morepreferably about 50 percent, by weight of binder components. Thepresence of zirconium silicate also increases the hardness, adhesion andacid resistance of finishes derived from these compositions and improvestheir heat transfer characteristics.

The stability of my compositions containing zirconium silicate and theblister resistance and hydrophobicity of coatings derived from them arealso enhanced if they contain from 0.1 through about 5 percent,preferably 0.5 through 1.5 percent, even more preferably about Ipercent, by weight of binder components, of hydrophobic silica (asdescribed above) or polydimethyl siloxane.

The corrosion protection provided by all of these zirconium silicatecontaining compositions, especially primers, can be even more improvedby adding to them from 50 through 900 percent, preferably 100-700percent, even more preferably -350 percent, by weight of bindercomponents, of particulate zinc (as described above).

My compositions can be made by adding suitable amounts of'all of thecomponents to a vessel and then pebble-milling or ball-milling theresulting mixture for from to 18 hours, or until the polyvinylidenefluroide is wetted and deagglomeratedThe resulting dispersion'willordinarily contain fromabout 50 to about on the surface to be coated. Itis an advantage of my compositions that they can be applied directly on.

treated or untreatedgrit blasted steel.

While one such coating gives good corrosion protection, I have foundthat my compositions give even better protection if three .ormoreseparate coats are applied, each about one mil thick (dry) and eachbaked after application for, 10 minutes at 400500F. The final coating ispreferably baked for .20 minutes at In cases where the-water to beheated is excessively acid or alkaline, or contains salts, I prefer toprime the metal substrate with one or more coats, preferably two, of acomposition which contains polyvinylidene fluoride, aminoplast resin,hydrophobic silica and zirconium silicate, all in a liquid carrier, asalready described, and which also contains 100-400 percent, preferably200 percent, by weight of the binder components,.of particulate zinc.This is then topcoated with one-or more coats of the same composition,preferably one, vbut lacking zinc.

While my compositions are most useful for coating the interior surfacesof water heater tanks, they are also useful for lining boilers, interiorsurfaces of pipes and drums, industrial containers, indeed any surfacewhich must come in contact with water at elevated tempera-.

tures or with corrosive materials.

DESCRIPTION OF THE PREFERRED EMBODIMENTS One skilled in the art will beable to practice my invention more easily after reading the followingillustrative ExampleslAll' parts are by weight.

EXAMPLE .1

This composition was pebble-milled until the solids were reduced to anaverage diameter of 1-2 mills.

The composition was reduced to spray viscositywith aromatic hydrocarbonand then applied in three separate coats to grit-blasted steel panels.The first two coats were applied to athickness of 1 mil (dry) and bakedfor 10 minutes at 475F. The third coat was applied at the samethickness, but baked for 20 minutes at The steel panels withstood 30days immersion in hot water (180F.) with no.0bservable deterioration ofthe coating or corrosion of the metal.

a I v EXAMPLE 2 g A composition was prepared bymixing togetherPolyvinylidene fluoride 227 parts Epon 1007 resin (as in Example I) 400parts Benzoguanaminc-formaldehyde resin (66% solids in n-butanol) I02.parts Diacetone alcohol 88 parts Solvesso 100 88 parts EXAMPL 3 A. Acomposition was prepared by mixing together Titanium dioxide l6.8l partsHydrophobic silica (Quso-Sl 0.34 part Polyvinyliderie fluoride 16.81parts Benz oguanamine-formaldehyde resin (66% solids in n-butanol) 7.63parts 1 Diacetone alcohol 14.5 parts Solvesso 150, l4.5 parts Epon 1007(as in Example I) 29.4 parts The resulting dispersion was pebble-milledfor about 18 hours and then reduced to spray viscosity with Solvesso150.

The composition was applied to steel panels as shown in Examplel, withsubstantially the same result.

B. In (A) above, titamium dioxide was replaced with an equal amount ofzirconium silicate and applied as in Example 1. r

The panel withstood immersion in a 10 percent aqueous NaCl solution at70C. for 6 months without blistering and with only slight discolorationof the film.

C. In (B), above, hydrophobic silica was replaced with the same amountof polydimethyl siloxane (Dow- Corning Co. 200 silicone), to give thesame result. Water on the surface of. the coating beaded into smalldrops.

EXAMPLE 4 as in Example 1, with substantially the same result.

B. To 65.6 parts of the dispersion in Example 3(B) were added 33.3 partsof zinc dust, 0.5 part of Solvesso and 0.5 part of diacetone alcohol.

This was processed as in (A) above and applied to a steel panel as inExample 1. The panel showed outstanding corrosion resistance.

phatetreated grit-blasted steel panel. Each coat was baked at 450for 10minutes.

This was then topcoated with one coat of the composition of Example 3(A)(1 mil thick dry) and baked 20 minutes at 475F.

This panel withstood more than 60 days immersion in softened water at180F., in a 3 hour cycle consisting of (l) emptying one-third of thecontainer contents, (2) refilling with water at room temperature, (3)reheating rapidly to 180F., with no observable deterioration of thecoating.

I claim:

1. Metal substrate bearing a cured coating deposited from a compositionconsisting essentially of A. 25-75 percent, by weigth of bindercomponents,

of polyvinylidene fluoride;

B. 20-60 percent, by weight of binder components,

of a condensation product of bisphenol A or bisphenol F andepichlorohydrin;

C. 5-25 percent, by weight of binder components, of

an aminoplast resin;

D. 0.1-5 percent, by weight of binder components, of

hydrophobic silica;

E. 5-100 percent, by weight of the binder components, of TiO and F. anorganic liquid carrier.

2. The metal of claim 1, in which the composition ad- 5 ditionallycontains 50-900 percent, by weight of binder components, of particulatezinc.

3. Metal substrate bearing a cured coating deposited from a compositionconsisting essentially of A. 25-75 percent, by weight of bindercomponents,

10 of polyvinylidene floride;

B. 20-60 percent, by weight of binder components,

of a condensation product of bisphenol A or bisphenol F andepichlorohydrin;

C. 5-25 percent, by weight of binder components, of

an aminoplast resin;

D. 0.1-5 percent, by weight of binder components, of

hydrophobic silica; E. 5-100 percent, by weight of the bindercomponents, of zirconium silicate; and F. an organic liquid carrier.

1. METAL SUBSTRATE BEARING A CURED COATING DEPOSITED FROM A COMPOSITIONCONSISTING ESSENTIALLY OF A. 25-75 PERCENT, BY WEIGHT OF BINDERCOMPONENTS, OF POLYVINYLIDENE FLUORIDE; B. 20-60 PERCENT, BY WEIGHT OFBINDER COMPONENTS, OF A CONDENSATION PRODUCT OF BISPHENOL A OR BISPHENOLF AND EPICHLOROHYDRIN; C. 5-25 PERCENT, BY WEIGHT OF BINDERCOMPONENTS,OF AN AMINOPLAST RESIN; D. 0.1-5 PERCENT, BY WEIGHT OF BINDERCOMPONENTS, OF HYDROPHOBIC SILICA; E. 5-100 PERCENT, BY WEIGHT OF THEBINDER COMPONENTS, OF TIO2; AND F. AN ORGANIC LIQUID CARRIER.
 2. Themetal of claim 1, in which the composition additionally contains 50-900percent, by weight of binder components, of particulate zinc.
 3. Metalsubstrate bearing a cured coating deposited from a compositionconsisting essentially of A. 25-75 percent, by weight of bindercomponents, of polyvinylidene floride; B. 20-60 percent, by weight ofbinder components, of a condensation product of bisphenol A or bisphenolF and epichlorohydrin; C. 5-25 percent, by weight of binder components,of an aminoplast resin; D. 0.1-5 percent, by weight of bindercomponents, of hydrophobic silica; E. 5-100 percent, by weight of thebinder components, of zirconium silicate; and F. an organic liquidcarrier.